The prior art includes a large number of receivers, sometimes called channel tuners. These devices are used for tuning to (i.e., receiving) a particular channel of a wideband signal--such as a wideband satellite signal, or a band of television signals transmitted through the atmosphere or via cable.
There are numerous circumstances in which it would be convenient to control a tuner with a computer which is also used for other purposes. For instance, it would be desirable to be able to use a personal computer to receive data transmitted on a particular satellite channel at a specified time.
Note that the present invention is not concerned with systems such as video cassette recorders which have a dedicated microcontroller inside the receiver, because such systems do not provide users with the broad range of data processing capabilities provided by microcomputers and larger computer systems.
Using currently available technology, it would be feasible to control an external tuner with a computer by transmitting control signals through one of the computer's ports, typically an RS232 serial port. The tuner in such a prior art system would be external to the computer for at least two reasons: (1) because tuners are traditionally located inside devices such as televisions, radios, and the like, and (2) because the RF (radio frequency) noise from the computer would interfere with the operation of the tuner.
It is well known to those skilled in the art that virtually all general purpose computers generate substantial amounts of RF noises. In the U.S. the amount of RF noise that can be generated by computer is regulated by the government. Nevertheless, the strength of the RF noise generated by even small computer systems is typically more than sufficient to corrupt weak signals, such as satellite signals picked up by a satellite antennae. Therefore prior art satellite receivers have been self contained, external units with their own power supply and control circuits.
It should also be noted that the amount of RF noise inside the housing of a typical computer is at least several orders of magnitude more than the RF noise measured external to the computer. Government RF noise regulations currently apply only to RF noise measured external to the computer.
Having the tuner external to the computer is a shortcoming because the tuner will need a separate power supply from the computer. Also, if the output of the tuner is data to be processed by the computer, an additional interface will be needed to coupled the output of the external tuner to the computer's data bus.
Another shortcoming of using an external tuner is that it is difficult to simultaneously control two or more tuners through a serial port. Of course, a special interface and protocol could be designed to control multiple external tuners through a single serial port, but this would also add to the expense of the system.
The present invention provides a channel tuner which is included inside a computer such as a personal computer. The channel tuner is coupled to the computer's bus so that commands can be sent to the tuner by directly sending data to one or more addresses corresponding to the tuner. If several tuners are provided, each is given a separate address in the computer's address space.
The channel tuner described herein can be housed inside the computer because the sensitivity of the tuner to RF radiation has been reduced through the use of low impedance circuitry, and also be shielding some of the tuner components from RF radiation.
Another feature of the present invention is that the d.c. power needs of the signal source, such as a satellite feed horn polarization controller, can be provided by the computer's own power supply. The power is transmitted to the signal receiver using the same cable used to transmit signals from the signal source to the tuner in the computer.
While the present invention is quite simple in concept, it substantially reduces the cost of satellite and other channel tuners, and it also substantially simplifies the delivery of transmitted data to a computer.